An Electromyographic Study on the Urethral Rhabdosphincter in Normal and Chronically Rhizotomized Cats: Analysis of Electrical Potentials Evoked by Sympathetic Nerve Stimulation

Abstract

To investigate functional aspects of sympathetic nerve influence on the urethral rhabdosphincter, we examined electrical potentials of the male feline rhabdosphincter evoked by hypogastric nerve (HGN) stimulation using electromyography. Hypogastric nerve stimulation (1 Hz) elicited electrical potentials of the rhabdosphincter in both normal and chronically rhizotomized cats. In normal cats, the evoked potentials were not affected by transection of the bilateral pudendal nerves. The amplitudes of the evoked potentials were significantly larger in rhizotomized cats (p < 0.001), while the threshold stimuli and latency periods were not. These evoked potentials were prazosin- and atropine-resistant, but were abolished by hexamethonium and pancuronium in both groups. In normal cats, high frequency stimulation (10 to 20 Hz) of the HGN increased the activity of the rhabdosphincter when the bladder was empty, but not when the bladder was full enough to trigger the vesicourethral relaxation reflex. This excitatory effect of HGN stimulation was blocked by prazosin. These data suggest that the potential of the rhabdosphincter evoked by HGN stimulation (1 Hz) is produced through synapse from sympathetic preganglionic to cholinergic postganglionic neurons, and that, after sacral rhizotomy, cholinergic postganglionic terminals form more effective functional connections to somatically denervated motor end-plates of the rhabdosphincter. The sympathetic nerve is also believed to play a role in modulating urethral afferent activities through action on urethral smooth muscle.